Method of rapidly determining the plasticity index of calcereous materials

ABSTRACT

The plasticity index of calcareous materials is rapidly determined by drawing up a quarry diagram representing the calcium carbonate percentages and plasticity indices of representative samples from a quarry producing the calcareous materials, wherein the samples contain a clay component from the same quarry ranging from about 5 to about 30 percent of the sample, and then determining the plasticity index of further samples of the calcareous materials by analyzing the samples for calcium carbonate content and reading the corresponding plasticity index on the quarry diagram.

limited tt [451 Sept. 17, M74

l /lelaicltrinos ME'rEIoo or E EmE DIETIEINIING Til-IE IPLASTICIITY INDEX oE CALCEIREUUS MATERIALS [75] Inventor: Basill). Melachrinos, Volos, Greece [73] Assignee: Theophanis Paraslteva, Seymour,

Conn.

22 Filed: Felb.22,l973

21 Appl.No.:334 ,949

[52] US. Cl. 23/230 R, 23/230 EP, 73/432 R [51] Int. CL. Gflln 33/24, GOln 33/38, GOln 33/42 [58] Field oil Search 23/230 R, 230 EP; 73/74,

[5 6] References Cited OTHER PUBLICATIONS 1965 Book of ASTM Standards, Part 11, Bituminous Materials for Highway Construction, Waterproofing, and Roofing; Soils; Skid Resistance; American Society PLASTICITY moex {P.i.) r r for Testing and Materials, Philadelphia, Pa. Pages 210 212, 1965.

Primary Examiner-Joseph Scovronek Assistant Examiner-Dale Lovercheck Attorney, Agent, or Firm-DeLio and Montgomery [5 7 ABSTRACT The plasticity index of calcareous materials is rapidly determined by drawing up a quarry diagram representing the calcium carbonate percentages and plasticity indices of representative samples from a quarry producing the calcareous materials, wherein the samples contain a clay component from the same quarry ranging from about 5 to about 30 percent of the sample, and then determining the plasticity index of further samples of the calcareous materials by analyzing the samples for calcium carbonate content and reading the corresponding plasticity index on the quarry diagram.

5 Claims, 2 Drawing Figures PELASGIA QUARRY DIAGRAM PAIENIEB SEPI 7am Gav xwazw PELASGIA QUARRY DlAQzRAM 1: Upm qim 8'5 C0 C0 (W PYRGOS QUARRY DIAGRAM QQQO5 ar a) XwOZM METHOD OF RAPIDLY DETERMINING THE lPLASTllCllTY INDEX OF CALCEREOUS MATERIALS BACKGROUND OF THE INVENTION This invention relates to the rapid determination of the plasticity index of calcareous materials.

Calcareous materials in an aggregate form are widely used as construction materials, or as components of construction materials, as in the construction of roads. In addition to qualitative content and particle size of the materials, a criterion for selection of suitable materials is the plasticity index of the materials. The plasticity index is the mathematical difference between the liquid limit and the plastic limit of the material (the socalled Atterberg Limits"). The Atterberg Limits are commonly determined experimentally according to standard procedures, such as the procedures adopted by the American Association of State Highway Officials (AASHO) under AASHO designations T89 and T90. The plasticity of the calcareous material is proportional to the percentage of clay content of the material in the quarry from which the material is obtained.

It is common practice to determine experimentally the Atterberg Limits, and'therefore the plasticity index, of numerous samples of calcareous aggregate materials from any given quarry, so that the usefulness of the material for construction purposes can be predetermined. However, the experimental determinations are based upon detailed procedures and the use of specialized laboratory equipment and therefore have required considerable time, of the order of days and even weeks, in which to develop sufficient information from which to judge the acceptability of all of the calcareous material from a given quarry. In addition, the plasticity indices thereby determined are affected by differences in experimental procedure of different laboratories and different laboratory technicians.

OBJECTS AND SUMMARY Accordingly, an object of the invention is to provide a new and improved method of determining the plasticity index of calcareous materials such thatnumerous such determination scan be 'made for materials from the same quarry in a relatively short period of time.

Another object is to provide a method for determining the plasticity index of calcareous materials which is substantially independent of individual factors, that is, differences in experimental technique of different laboratories and technicians.

These and other objects, features and advantages of the invention will be apparent from the specification which follows.

In brief outline, the method of the invention is based upon the discovery that by a few initial determinations of calcium carbonate content and plasticity index on samples of calcareous materials admixed with various amounts of clay from the same quarry, a quarry dia gram can be drawn up with the plasticity indices and calcium carbonate percentages as coordinates. Thereafter, for determinations of the plasticity index of additional samples from the quarry, the technician has only to analyze the sample for calcium carbonate content and then read on the quarry diagram the plasticity index corresponding to the calcium carbonate content.

Accordingly, the method permits numerous and rapid determinations of plasticity index of new samples of the calcareous material, which determinations are essentially independentof individual differences in experimental procedure.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, which will be. exemplified inthe method hereinafter disclosed, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference is had to the following description taken in conjunction with the accompanying drawing in which:

FIGS. 1 and 2 are graphs of plasticity index versus calcium carbonate content of two quarries in Greece, representative of application of the method of the invention.

DETAILED DESCRIPTION For construction uses, the chief characteristics of quarry limestone aggregates which must be determined are the particle size (grading) and the plasticity. The latter is most often indicated as "the Plasticity Index (PI), which is the mathematical difference between the liquid limit and the plastic limit of the material. The liquid and plastic limits are also known as the Atterberg Limits. One widely accepted method of determining the Atterberg Limits is that adopted by the American Association of State andl'lighway Officials (AASHO) under the AASHO designations T89 (Liquid Limit) and T90 (Plastic Limit and Plasticity Index). Substantially identical to these procedures are the standard methods adopted by the American Society For Testing And Materials (ASTM) under the ASTM designations D423 and D424.

The plasticity of the calcareous aggregate material is due primarily to the plasticity of the clay strata of the quarry from which the material is taken. It is therefore well known that the plasticity of the calcareous material is proportional to the percentage of the clay content and depends on the consistency and properties of the clay, for example, whether the clay be thin, thick, colloidal or non-colloidal.

In the practice of the method of the invention, advantage is taken of the standard procedures for determining the plasticity index and calcium carbonate content but the procedures are carried further in that a quarry diagram is prepared based upon initial plasticity index and calcium carbonate content determinations. The quarry diagram is prepared according to the following description.

A plurality of representative samples of calcareous material is taken from the quarry for which the quarry diagram is to be prepared. The samples are cleaned according to known procedures so as to be substantially free of clay. If necessary, the samples are broken up and the material having a predetermined sieve size is analyzed according to known procedures for calcium carbonate content. The purpose of the analysis is to assure that the calcium carbonate content of the material from various sections of the quarry is sufficiently uniform so that the subsequent steps of the method can be applied. Variation of calcium carbonate content within plus or minus about 1 percent is generally acceptable. In some instances this first determination of calcium carbonate content may be avoided, for example, where the required uniformity of calcium carbonate content is already well known.

The method for determining calcium carbonate content may be the well known volumetric technique wherein a fixed amount of hydrochloric acid is reacted with the material and the amount of unreacted acid is determined by neutralization with an alkali. Other techniques obviously may also be employed for this determination, if desired.

The analysis for calcium carbonate content (and Atterberg Limits as described below) is generally performed on aggregate material of a standard sieve size, preferably a sieve No. 40, as described in the aboveidentified AASHO test procedures.

Clay materials are then taken from the same quarry. If not sufficiently dry, the samples are crushed and airdried. The component of the same sieve size as the above-described calcareous material, preferably sieve No. 40, is taken. The clay material is cleaned sufficiently so that it is substantially free of calcareous material.

The thus-obtained clay is admixed with the calcareous material of the same particle size from the same quarry to provide a plurality of mixtures containing from about 5 percent to about 30 percent by weight of the clay. The calcium carbonate content and Atterberg Limits of each mixture are then determined according to the standard methods referred to above, or by other methods. From the resultant data the plasticity index of each mixture is calculated and plotted against the corresponding percentage of calciumcarbonate, to produce a quarry diagram. Preferably, the percentage of calcium carbonate is plotted as the abscissa and the plasticity index (P.I.) is plotted as the ordinate. One of the surprising discoveries of the present invention is that the resulting plot describes an essentially linear relationship between the plasticity index and the calcium carbonate content, the linearity representing an inverse proportionality between the plasticity of the material and the calcium carbonate content.

The quarry diagram can then be used to quickly provide the plasticity index of other samples of calcareous material from the same quarry. This is achieved simply by analyzing the new samples for calcium carbonate content, as already described, and then locating on the quarry diagram the plasticity index corresponding to the calcium carbonate content.

Prior to the present invention, the plasticity index of each sample of material from the quarry had to be independently determined, by long and tedious experimental procedures for the determination of the Atterberg Limits, and the results were often adversely affected by differences in experimental technique as between different technicians and different laboratories. Now it is possible on the basis of a relatively few determinations of Atterberg Limits, of the order of about four to ten such determinations, to provide basis for all further required determinations of plasticity index. Accordingly, by practice of the method of the invention, a single laboratory technician can now determine in a single working day the plasticity index of some 60 to 80 samples of calcareous aggregate, an achievement that formerly required several weeks of effort.

EXAMPLE The following is an actual description of experimental procedures whereby the quarry diagrams of FIGS.

1 and 2 were obtained. In this example, and throughout this specification and claims, all parts and percentages are by weight unless otherwise indicated.

Representative samples of limestone calcareous material were taken from each of Pelasgia Quarry and Pyrgos quarry in the District of Volos, Greece. The samples were cleaned so that they were substantially free of clay and other non-calcareous impurities and were then broken up. The calcareous material passing through a sieve NO. 40 was then collected and its content of calcium carbonate volumetrically determined (as described above) to assure that the calcium carbonate content of all of the samples was within acceptable limits for uniformity for the subsequent determinations.

Clay was then also taken from each of the quarries, cleaned to make it substantially free of calcareous material, and then air-dried and crushed. The clay component passing through a sieve No. 40 was then taken and uniform mixture of the clay with the calcareous material of the same size from the respective quarries were prepared to provide a plurality of mixtures ranging in clay content of from about 5 percent to about 30 percent by weight. The resulting mixtures are listed in Tables 1 and 2 below.

Calcium carbonate content and Atterberg Limits were determined for each of the components of mixtures and the mixtures themselves, and the plasticity index of each calculated where possible. At the same time, the clay component was quantitatively analyzed (optional). All of the resulting data is set forth in Tables l and 2 following. In each instance the Atterberg Limits were determined by AASHO procedures T89 and T90.

TABLE 1 Pelasgia Quarry Samples Wgt. of Clay Added Liquid Plastic Plasticity To Calcareous Wgt. Limit Limit Index Aggregate CaCO (L.L) (P.L.) (P.l.)

Non- 5 92.25 Plastic 10 87.75 19.50 14.50 5.00 15 83.50 22.00 13.00 9.00 20 79.00 25.30 11.30 14.00 25 74.50 31.20 12.20 19.00 30 69.90 36.00 12.00 24.00

Aggregate Without Added Clay 97.10

Clay Alone 4.00 109.50 29.50 80.00

Analysis of Clay Component Si 0 53.23% A1 0 24.40% 1 2.60%

TABLE 2 Pyrgos Quarry Samples Liquid Plastic Plasticity Wgt. Limit Limit Index CaCO; '(L.L.) (P.L.) (P.l.)

92.00 Non-Plastic 87.75 Non'Plastic 83.25 21.00 16.00 5.00

TABLE 2-Continued Pyrgos Quarry Samples Analysis of Clay Component s1 0 A1 0 Fe O Quarry diagrams for each of the quarries were then drawn up, as shown in the accompanying FIGS. 1 and 2. The significant portion of the curve of each Figure is that above the plasticity index of 5, since this is the portion that represents calcareous materials most useful in road construction. It will be noted that in each in stance the plot is essentially linear, representing a surprising uniformity of relationship between plasticity index and calcium carbonate content for each quarry. Accordingly, on the basis of the quarry diagrams, the plasticity index of additional samples of material of each of the quarries may be rapidly and conveniently determined simply by analyzing sieve No. 40 samples of the material for calcium carbonate content and finding the plasticity index corresponding to each sample on the quarry diagrams.

The quarry diagrams were verified as to accuracy by experimental determination on numerous samples over a long period of time. One of the means of verification was by known tests for the sand equivalent on the crushed calcareous aggregate materials and the relating of the sand equivalent to the plasticity index. These verifications are indicated on each of the curves of lFlGS. ii and 2 by X marks, the remaining points indicated on each of the plots representing the data of Tables l and 2.

While the invention has been illustrated and described in what are considered to be the most practical and preferred embodiments, it will'be recognized that many variations are possible and come within the scope thereof, the appended claims therefore being entitled to a full range of equivalents.

What is claimed is:

ll. A method of rapidly determining the plasticity index of calcareous materials from a quarry producing such materials, comprising:

a. obtaining from said quarry a calcareous material and preparing therefrom an aggregate substantially free of clay and having a predetermined sieve size;

b. obtaining from the same quarry a clay material and preparing therefrom a component substantially free of calcareous material and having the same said predetermined sieve size; c. admixing said calcareous aggregate and said clay component to form a plurality of mixtures ranging in content of said clay component of from about 5 percent to about 30 percent by weight; d. determining the calcium carbonate percentage and the plasticity index of each said mixture and plotting said determinations to produce a quarry diagram of said quarry; and e. determining the plasticity index of other samples of calcareous material from said quarry by determining the calcium carbonate percentages of aggregates thereof having the same said predetermined sieve size, and reading the coordinate plasticity index values on said quarry diagram. 2. A method as in claim 1 wherein said sieve size is No. 40.

3. A method as in claim 1 wherein the calcium carbonate percentages of a plurality of aggregate samples of step (a) are determined.

4. A method as in claim 1 wherein the aggragate of step (a) is prepared by breaking up and cleaning said calcareous material.

5. A method as in claim ll wherein the clay material of step (b) is cleaned, air-dried and pulverized to pro duce said component.

l l= l UNITED STATES PATENT OFFICE CEHHFICAIE OF CORRECTION Patent No. 3 836 330 Dated Sep cember l7 19 74 lnventflsj Basil D. .Melachrinos I It is certified that error apoears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

in Column 1', line 46, "determination scan" should read I determinations can Column 4, line 20, "mixture" should read mixtures Claim 4, line 1, "aggregate" should read aggregate l Signed and sealed this 3rd day of December 1974.

(SEAL) Attest: v

McCOY M. GIBSON JR. C. MARSHALL DANN A'ctesting Officer Commissioner of Patents 

2. A method as in claim 1 wherein said sieve size is No.
 40. 3. A method as in claim 1 wherein the calcium carbonate percentages of a plurality of aggregate samples of step (a) are determined.
 4. A method as in claim 1 wherein the aggragate of step (a) is prepared by breaking up and cleaning said calcareous material.
 5. A method as in claim 1 wherein the clay material of step (b) is cleaned, air-dried and pulverized to produce said component. 